Effects of bethanechol on canine urinary bladder smooth muscle function.

We studied whether the effects of bethanechol are mediated via a muscarinic receptor, the role of extracellular calcium on bladder contraction, and down-regulation of bladder contraction by bethanechol after activation with potassium chloride (KCl) and acetylcholine (Ach). Smooth muscle strips of normal urinary bladder were studied with standard methods to measure isometric force. Bethanechol caused a dose-dependent increase in bladder contraction. The potency of bethanechol is higher than Ach, as shown by higher peak active isometric stress (P(max)) and lower half-maximal contraction (ED(50)) (P< 0.01). The contractile responses to bethanechol were diminished in the presence of atropine, nifedipine and in calcium-free medium as shown by P(max) decreased by 58%, 87% and 65% and ED(50) increased by 314-, 24- and 16-fold, respectively. When bladder strips were stimulated with KCl and Ach, pre-treatment with bethanechol reduced the responses to KCl by 116-242% (P<0.05), while the contractile responses to Ach were unaltered. Thus, bethanechol induces bladder contraction via muscarinic receptor activation while both intracellular and extracellular calcium play a crucial role on bladder smooth muscle contraction. The mechanisms of down-regulation by bethanechol may be related to interference with calcium influx into the smooth muscle cells, rather than the desensitisation of muscarinic receptors or post-receptor steps of signal transduction following bethanechol binding to the receptor.

Norepinephrine kinetics in dogs with experimentally induced renal vascular hypertension.

OBJECTIVE: To determine norepinephrine (NE) kinetics in dogs with experimentally induced renal vascular hypertension. ANIMALS: 4 mixed-breed dogs. PROCEDURE: The study comprised a control and hypertensive period. The hypertensive period followed induction of renal vascular hypertension achieved by surgical placement of clips on both renal arteries to reduce diameter by approximately 80%. Arterial blood pressure, renal clearance, and NE kinetics were measured during each period while dogs were receiving a low-sodium diet. Measurements of NE kinetics and renal clearance during the hypertensive period were made 5 days after induction of hypertension. RESULTS: Five days after induction of hypertension, arterial blood pressure increased by 15 to 20 mm Hg. Mean (+/- SEM) plasma NE concentration and NE spillover rate increased significantly from 151.5+/-14.1 pg/ml and 8.03+/-0.62 ng/kg/min, respectively, during the control period to 631.4+/-30.5 pg/ml and 54.0+/-5.2 ng/kg/min, respectively, during the hypertensive period. Norepinephrine clearance rate also increased (54.0+/-2.4 vs. 86.0+/-9.3 ml/kg/min). Positive associations between mean arterial pressure (MAP) and NE concentration and spillover rate were detected. However, MAP and NE clearance rate were not associated. CONCLUSIONS AND CLINICAL RELEVANCE: Increased blood pressure during the hypertensive period was likely attributable to increased NE spillover rate, which resulted in a significant increase in plasma NE concentration. Analysis of these results suggests that central sympathetic outflow was increased and may be responsible for the pathogenesis of high blood pressure during the acute phase of renal vascular hypertension in dogs.

Evaluation of change in blood flow by contrast-enhanced power Doppler imaging during norepinephrine-induced renal vasoconstriction.

We evaluated the changes in flow induced by intrarenal infusion of norepinephrine by an ultrasonographic contrast agent and power Doppler imaging. Hypoperfusion was induced in dogs (N = 5) by infusing norepinephrine directly into the renal artery for 30 min at doses of 0.7 microg/kg/min, 1.0 microg/kg/min, and 1.9 microg/kg/min. Contrast agent injections were made before and after each infusion of norepinephrine. The transit of contrast agent through the kidney and color enhancement were measured by computer analysis of power Doppler images. Mean transit time and effective renal plasma flow were measured. The effective renal plasma flow decreased by 29%, 30%, and 64%, respectively, with the increasing doses of norepinephrine. Paralleling this change, the mean transit time, which corresponds to reduction in renal blood flow, increased by 26%, 43%, and 77%, respectively, from the preinfusion value. Regression analysis shows renal blood flow to decrease exponentially with norepinephrine dose. Renal blood flow changes measured by contrast-enhanced imaging correlated closely with the effective renal plasma flow measurements. Computer analysis of contrast-enhanced power Doppler images allowed measurement of renal blood flow. This technique may be useful in assessing renal perfusion during pharmacologic and other therapeutic interventional procedures.

Comparison of power Doppler and B-scan sonography for renal imaging using a sonographic contrast agent.

The goal of this study was to evaluate the relative performance of power Doppler and B-scan imaging modes in detecting vascular perfusion changes resulting from injection of a contrast agent. To allow this comparison the imaging plane and the contrast agent injection must be the same for both modes. We achieved this by using a rigid transducer holder and simultaneously recording power Doppler and B-scan images on separate videotapes. The kidneys of five adult beagles were scanned to allow a comparison of how power Doppler and B-scan imaging methods monitor changes during the injection of 0.1 ml/kg of a contrast agent, EchoGen emulsion (Sonus Pharmaceuticals, Bothell, WA). The changes in the images were assessed qualitatively by three radiologists and quantitatively using a custom-designed image analysis software. All of the radiologists agreed that no visually detectable changes occurred in B-scan images but that significant changes could be observed in power Doppler images. Image analysis also indicated a difference between power Doppler and B-scan images. The change in mean color level of power Doppler images could be displayed as an indicator dilution curve with a peak enhancement of 46 +/- 16 above the preinjection value. The time at which mean color level peaked was 18 +/- 13 s. The mean color level returned to half of the peak value by 69 +/- 42 s and returned to the preinjection baseline value by 148 +/- 73 s. Conversely, B-scan images showed statistically insignificant changes, and time measurements could not be made. By all measures used to evaluate images, power Doppler imaging had a greater sensitivity in detecting changes resulting from contrast agent injection than B-scan imaging. This finding indicates that power Doppler imaging of contrast agent injections can be used to map regional differences in flow as well as quantitative measurements of a contrast agent's transit time and has the potential to assess kidney abnormalities associated with renal blood flow.

Comparison of direct and indirect (oscillometric) measurements of arterial blood pressure in conscious dogs.

Oscillometric measurements of arterial blood pressure were compared with direct measurements made on seven dogs fitted with catheters. Tail and limb cuff sites were used while the dogs were gently restrained either standing or in lateral recumbency. The accuracy of the readings for the various cuff sites was compared with the direct (gold standard) readings. The accuracy of the indirect readings was improved by using mean values from a series of readings rather than individual values and when the dogs were in lateral recumbency rather than standing. The differences between the direct and indirect values were greatest with high pressures, and with systolic rather than diastolic values. In standing dogs, the proximal forelimb readings (when obtainable) correlated most closely with the direct readings. The tail cuff readings correlated significantly with the direct readings, though less closely. The tail cuff readings were the most easily recorded in the standing dogs. In the laterally recumbent dogs, the readings from all the cuff sites correlated closely with the direct values except for diastolic readings from the distal hindlimb.

Inheritance of cystinuria and renal defect in Newfoundlands.

OBJECTIVE: To describe clinical features, characterize metabolic renal abnormalities, and evaluate mode of inheritance of cystinuria in Newfoundlands. DESIGN: Prospective study. ANIMALS: Two families of Newfoundlands including 11 dogs with dysuria, stranguria, or obstruction attributable to cystine calculi. PROCEDURE: Urinalysis and nitroprusside spot tests were performed to evaluate cystinuria in the affected dogs. All calculi were analyzed by crystallography. Amino acid concentrations in urine and plasma of affected dogs were compared with those in clinically normal related dogs. Renal fractional excretion and reabsorption of amino acids were determined in 5 affected Newfoundlands. RESULTS: Nine dogs had pure cystine calculi in the bladder, and 4 of these had renal cystine calculi. Affected dogs persistently excreted excessive amounts of cystine (> 500 nmol/mg of creatinine; reference = 54 +/- 38 nmol/mg of creatinine) and had typical cystine crystals in acidic urine. Urinary excretion of ornithine, lysine, and arginine was also high. Dogs with cystinuria had complete lack of reabsorption and active secretion of cystine, and reabsorption of lysine, ornithine, and arginine was moderately impaired. Although clinical signs of urinary obstruction were observed only in males, cystinuric male and female offspring were produced from noncystinuric parents, consistent with an autosomal recessive mode of inheritance. Obligate heterozygotes did not have clinical signs, and had normal urinary cystine content and renal amino acid reabsorption. CLINICAL IMPLICATIONS: Because detection of carriers by routine urinalysis is currently not possible, Newfoundlands with cystinuria and their parents and offspring should be excluded from breeding.

Renal brush border membrane lipid composition in Basenji dogs with spontaneous idiopathic Fanconi syndrome.

To comprehend the renal defect underlying idiopathic Fanconi syndrome in the Basenji dog, we have focused on delineating the lipid profiles of renal brush border membranes isolated from affected and normal Basenji dogs to establish any physical or compositional changes underlying previously observed transport and membrane-fluidity changes. The lipid composition was studied with respect to total lipid, cholesterol, and phospholipid content, cholesterol to phospholipid ratio, distribution of the major phospholipid classes, and fatty acid composition. Total phospholipid of the isolated renal brush border membranes from Fanconi syndrome dogs analyzed by 31P nuclear magnetic resonance showed no difference compared with that of normal dogs. Examination of total fatty acids in both membranes using gas-liquid chromatography analysis of fatty acid methyl esters showed no difference in the mole percents of the major fatty acids. Our data suggest that changes in bulk membrane fluidity of the Fanconi syndrome dog renal brush border as measured by 1,6-diphenyl-1,3,5-hexatriene cannot be attributed to phospholipid and fatty acid compositional change. In the membranes isolated from affected dog kidney, the cholesterol content determined by gas-liquid chromatography analysis was 66 mol% higher than in membranes isolated from normal dog kidney. This correlates with the higher cholesterol to phospholipid molar ratio of 0.82 +/- 0.08 in the affected animal as compared with 0.58 +/- 0.04 in the normal. Cholesterol content and its microdomain in the membrane bilayer may be important in modulating transport functions. Increased membrane cholesterol content may affect the conformational motility of membrane transport proteins and thus affect their function.

Chronic pressure-natriuresis relationship in dogs with inherited essential hypertension.

A genetic model of essential hypertension in the dog was studied to describe the phenotypic expression of the arterial pressure, as well as to determine the relationship between mean arterial blood pressure (MAP), hormone, and renal excretory responses to four different levels of sodium intake (5, 40, 120, 240 mEq/day) delivered intravenously and isotonically. This model was developed at the University of Pennsylvania (U/Penn) and termed Pennsylvania hypertensive dogs (PHD). The MAP was recorded beat-by-beat, 24 h/day, in 16 dogs. Water and sodium balances were determined daily for 4 days at each level of intake and blood samples were collected on the last day of each salt step for analysis of plasma renin activity (PRA), atrial natriuretic peptide (ANP), aldosterone (ALDO), and vasopressin (AVP). After the study, the dogs were designated as hypertensive (PHD-HT) when the 24-h average MAP was greater than 110 mm Hg and systolic pressure was greater than 160 mm Hg. Dogs that failed to meet both criteria were designated as normotensive genetic controls (PHD-NT). Although sodium was retained during the first day of each increase of salt intake in both groups, a return to balance was observed within the 4 days. There was no apparent change in the slope of the chronic renal function curve in either group of PHD studied, although the PHD-HT exhibit a curve shifted to a higher level of MAP. Plasma hormone levels in both groups of PHD studied responded in a manner similar to normal mongrel dogs with reductions of PRA, ALDO, elevations of ANP, and no change in AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane fluidity and sodium transport by renal membranes from dogs with spontaneous idiopathic Fanconi syndrome.

To comprehend the renal defect underlying the idiopathic Fanconi syndrome in the Basenji dog, we have used isolated renal brush border membrane vesicles to examine two factors that influence membrane nonelectrolyte transport processes, sodium flux and membrane fluidity. We have found that there is no significant difference in the rate of uptake of 100 mmol/L 22Na+ and conclude that the previously observed defects in the sodium gradient-stimulated overshoot of glucose and of proline are not related to an alteration in the flux of sodium at physiological concentrations. Since carrier proteins exist in a lipid milieu, alteration in the physical state of the lipid membrane can determine transport function. Renal brush border preparations from normal and affected animals were studied by measuring fluorescence polarization to assess differences in the physical state of the membranes using the fluorescent probe, DPH, which quantitates inner core membrane fluidity. Membranes from affected dogs consistently showed a higher fluidity as measured by eta, a parameter of DPH fluorescence polarization. Since membrane fluidity is related to lipid composition, the data suggest that there may be an important alteration in the lipids in renal membranes of affected animals.

Influence of dietary protein on renal function in dogs.

Two previously published studies in dogs with reduced renal function are reviewed. In the first study, renal function and biochemical responses to dietary changes were studied in four dogs with stable chronic renal failure. The objective was to determine if dogs with moderate stable failure adjust to diets with varied protein and electrolyte content. These dogs were found to have the capacity to adapt to a wide range of dietary protein and electrolyte intake. The only exception was found in dogs fed a reduced-protein diet, which failed to appropriately adjust renal tubular excretion of sodium and phosphate. The only advantage of reduced dietary protein in this study was a reduction in blood urea nitrogen (BUN). Disadvantages of reduced-protein diets were reduced glomerular filtration rate (GFR) and renal plasma flow. In the second study, the hypothesis that large amounts of dietary protein sustain renal hyperfunction and produce progressive glomerulosclerosis in dogs as previously reported in rats was tested. Results failed to find a pattern of deterioration of renal function over 4 y. Light microscopic changes and electron microscopy also failed to find glomerular injury similar to that reported in rodents. These results do not support the hypothesis that feeding a high protein diet had a significant adverse effect on renal function or morphology.

Cholecalciferol rodenticide intoxication in a cat.

A 4-month-old 2.5-kg sexually intact female domestic shorthair cat was referred to the teaching hospital because of suspected cholecalciferol intoxication after ingestion of a cholecalciferol-containing rodenticide. At referral, the cat was hypercalcemic, hyperkalemic, and acidotic. Despite management of hypercalcemia and preservation of renal function with physiologic saline solution, furosemide, dopamine, and calcitonin, the cat died, apparently as a result of extensive pulmonary mineralization.

Effects of the nonpeptide angiotensin II receptor antagonist DuP 753 on blood pressure and renal functions in spontaneously hypertensive PH dogs.

A colony of genetic hypertensive dogs with systolic blood pressure of 140 to 220 mm Hg and diastolic blood pressure greater than 100 mm Hg in the trained state was used. The objective of this study was to investigate the hemodynamic and renal effects of the novel angiotensin II receptor antagonist DuP 753 given intravenously to these dogs. Renal functions and blood pressure were measured 45 to 75 min after the intravenous administration of DuP 753 at 1, 3, 10, and 30 mg/kg and were compared to control (placebo) treatment. Arterial pressure was slightly but significantly and dose-dependently reduced by DuP 753. Glomerular filtration rate increased significantly in a dose-dependent manner. Similarly, effective renal plasma flow was dose-dependently increased. Filtration fraction was unchanged. Renal vascular resistance was significantly reduced in a dose-dependent manner at 3, 10, and 30 mg/kg of DuP 753. DuP 753 increased fractional sodium excretion at all doses and increased fractional potassium excretion only at the highest doses. The vasopressor effects of angiotensin I and II were dose-dependently inhibited by DuP 753. These data show that DuP 753 has beneficial renal hemodynamic effects and lowers arterial pressure in this canine model of essential hypertension.

Essential hypertension in a dog.

Severe hypertension was diagnosed in a dog that initially was referred for evaluation of visual deficits and retinal hemorrhage and eventually was donated for medical treatment of hypertension. Initial blood pressure measured by direct methods was markedly high (systolic, 275 mm of Hg; diastolic, 170 mm of Hg). Measures of renal function were within normal limits, with the exception of hypotonic urine. A test protocol was designed to exclude possible secondary causes of hypertension; negative results of such tests allowed the diagnosis of essential hypertension. The consistency of the hypertension and its response to medical control were studied for 5 years. Blood pressure while the dog was untreated during those years was 240 +/- 24 mm of Hg (systolic) and 146 +/- 14 mm of Hg (diastolic). Plasma renin activity was within normal limits, and the response of the renin-angiotensin system to varied salt intake was normal. The most effective medications used to lower blood pressure were propranolol and captopril, both of which were more effective than salt restriction alone. Five years after the diagnosis of hypertension, the dog was euthanatized because of chronic renal failure secondary to pyelonephritis. Hypertension was less severe as the condition progressed into chronic renal failure. Complete necropsy did not reveal an obvious cause of the hypertension, and histopathologic changes were limited to the cardiovascular system, eyes, and kidneys.

Cystinuria in dogs: comparison of the cystinuric component of the Fanconi syndrome in basenji dogs to isolated cystinuria.

Two animal models for cystinuria have been examined: the Basenji dog with Fanconi syndrome and cystine stone-forming dogs of various breeds. Brush-border membranes were isolated from these animals and uptake of D-glucose and L-cystine was characterized. Experiments with isolated brush-border vesicles from Basenji dogs with cystinuria as a component of the Fanconi syndrome showed diminished sodium-dependent D-glucose uptake but no decrease in L-cystine uptake even though the cystine defect in vivo was as high as 94% (ie, 6% reabsorption). In contrast, brush-border vesicles isolated from the kidney of a cystine stone-forming dog (Welsh Corgi) with a cystine defect of only 16% (ie, 84% reabsorption) had decreased uptake of cystine compared to values found for Beagle and Basenji vesicles. Thus, cystinuria found in Basenji dogs with the Fanconi syndrome differs from that in classic stone-forming cystinuric dogs. The alteration responsible for the cystinuria of Basenji dogs with Fanconi syndrome does not appear to have a membrane locus and may reflect altered energetics for transport, which are not detected in isolated vesicles. The cystine defect in cystinuric stone-forming dogs does appear to be reflected in the isolated membrane.

Renal dysfunction in dogs with pyometra.

Renal function and pathologic changes in 27 dogs with pyometra were studied. Evaluation included CBC; serum biochemical evaluation; urinalysis; urine and uterine bacteriologic culture; uterine morphologic features; and light, electron, and immunofluorescent microscopic evaluation of renal tissues. Measurements of 24-hour creatinine clearance, protein excretion, Na excretion, and urine volume were made in 12 dogs without azotemia. Of 27 dogs, 26% were azotemic and 89% had a urine sp gr less than 1.035. Glomerular filtration rate was reduced in 75% of 12 dogs without azotemia. None of these 12 dogs was proteinuric. Examination of renal biopsy specimens revealed a high prevalence of mild tubulointerstitial nephritis, but few specific glomerular lesions. Minimal immunofluorescence was detected within the mesangium in 18% of the dogs. Immunofluorescence was not associated with the interstitium or tubules. Urinary tract infection was detected in 22% of the dogs. Escherichia coli and Klebsiella were recovered from the uterus in 59 and 15% of the dogs, respectively. Low urine specific gravity values were obtained from dogs without azotemia and from dogs with uterine cultures considered negative for E coli and other gram-negative bacteria. The reduction in glomerular filtration rate was a functional abnormality not correlated with structural damage in the glomerulus.

Spontaneous systemic hypertension in dogs: five cases (1981-1983).

Spontaneous (not experimentally induced) systemic hypertension was detected in 5 male dogs that were examined because of apparent blindness caused by intraocular hemorrhage and/or retinal detachment. Secondary causes of hypertension, including renal, adrenal, and thyroid disease, were investigated. Four of the dogs had glomerulonephropathy, renal insufficiency, and proteinuria. Four dogs had compensatory cardiac hypertrophy. Hypertension in 4 of 5 dogs was associated with glomerulosclerosis with chronic renal insufficiency, bilateral adrenocortical hyperplasia, adrenocortical adenoma with renal amyloidosis, and immune-mediated glomerulonephritis with chronic renal insufficiency, respectively. The fifth dog was determined to have essential hypertension. The dogs were treated for their primary diseases. Sodium restriction alone was inadequate to reduce blood pressure; 4 of the dogs also required antihypertensive medications.

Ureterocolonic anastomosis in clinically normal dogs.

Ureterocolonic anastomosis was evaluated in 13 clinically normal dogs. Urinary continence was maintained after surgery, and the procedure was completed without technique errors in all but 2 dogs. Three dogs died within 5 weeks (2 of undetermined causes and 1 of aspiration pneumonia and neurologic disease), and 1 dog was euthanatized 4 months after surgery because of neurologic signs. Two healthy dogs were euthanatized 3 months after surgery for light microscopic evaluation of their kidneys. Five dogs were euthanatized 6 months after surgery for light microscopic evaluation of their kidneys. Gastrointestinal and neurologic disturbances developed in 4 dogs at various postoperative intervals. Plasma ammonia concentration measured in 2 dogs with neurologic signs was increased. Plasma ammonia concentration measured in 5 dogs without neurologic signs was within normal limits. All 5 dogs, in which metabolic acidosis was diagnosed, had high normal or above normal serum chloride concentration. Serum urea nitrogen values were increased after surgery because of colonic absorption of urea. Serum creatinine concentration was increased in 1 dog 6 months after surgery. Individual kidney glomerular filtration rate was reduced in 38% (3/8) of the kidneys from 4 other dogs at 6 months after surgery. Of 5 dogs euthanatized at 3 to 4 months after surgery, 4 had bilateral pyelitis, and 1 had unilateral pyelonephritis. Six months after surgery, pyelonephritis was diagnosed in 40% (4/10) of the kidneys from 5 dogs. The ureterocolonic anastomosis procedure is a salvage procedure that should allow complete cystectomy. However, variable degrees of metabolic acidosis, hyperammonemia, and neurologic disease may result.

Hypertension and renal function.

The presence of hypertension in domestic animals is poorly described. Values for hypertension were established in dogs using a direct blood pressure measurement. A protocol was devised to recognize and characterize primary (essential) and secondary hypertension. Essential hypertension was associated with marked elevations in blood pressure and can be shown to be a hereditary disease in dogs. Secondary hypertension is more common and most frequently associated with Cushing's disease and renal failure. Treatment to reduce blood pressure in both groups can be achieved using pharmacologic agents which are more effective than sodium restriction alone. Hypertension appears to be an underdiagnosed disease in dogs. The significance of chronic hypertension in dogs in terms of vascular pathology is not yet clear.